1. Field of the Invention
The present invention generally relates to a digital measurement apparatus and an image measurement apparatus, and, in detail, to data security of an apparatus which converts an input obtained through a digital camera, a sensor, a FAX (modem) or the like into digital data, and performs processing such as management, transmission or the like on the digital data.
2. Description of the Related Art
Recently, conversion of information into electronic data has been rapidly progressing. This information, as electronic data, has been transmitted via a network or a portable medium, and various techniques have been developed for securing the electronic data. The electronic-data security techniques generally studied include a data concealment technique, a data-falsification detecting technique, a technique for management (including authentication) of access right to data, and so forth, in which techniques data is treated as merely a batch and the contents of the data are not aimed at. Techniques concerning whether or not the contents of the electronic data are correct have not been aggressively developed. However, when original data to be secured is wrong, there is no sense in securing the data. In the related art, when original data is generated electronically, processing such as addition of a digital signature of a person who produced the data or a person who has responsibility for the data may be performed in order to guarantee that the contents of the data are correct.
U.S. Pat. No. 5,499,294 (Friedman) and ‘The Trustworthy Digital Camera: Restoring Credibility of the Photographic image’ of Friedman, IEEE Transaction on Consumer Electronics, Vol. 39, No. 4, November 1993 disclose a method in which a private key unique to a digital camera is stored in the digital camera, the private key is used for calculating a digital signature for an image file taken by the digital camera, and the calculated digital signature is stored in a medium together with the image file. In detail, the private key stored in the digital camera is recorded in a ROM in a secure processor in the digital camera, and cannot be read externally. Further, a public key corresponding to the private key is put as a seal on the housing of the digital camera. Furthermore, the public key and parameters indicating the photography situation and so forth are arranged on the periphery of an image taken by the digital camera, and the digital signature is put on the thus-obtained entire image. Thereby, the credibility (ability to be used as evidence) of the image taken by the digital camera is improved. It is supposed that the public key corresponding to the digital camera is made wide open to the public by the manufacturer of the digital camera.
However, according to the above-described prior art, because the image file and the digital-signature file calculated by the digital camera are separate, there is a possibility that relationship between them becomes unrecognizable when these files are moved to a personal computer or the like. Therefore, although the processing for improving the credibility of the image file was performed, it cannot be recognized which digital signature corresponds to the image file, and, thereby, it becomes impossible to verify the integrity of the image file.
Further, in this prior art, a pair of a private key and a public key is generated by the manufacturer of the digital camera, and is recorded inside of the digital camera. However, the fact that the manufacturer of the digital camera knows the private key results in degradation of the credibility of the image file.
Further, in this prior art, after a timer built in the digital camera is set at the time of manufacture, the setting cannot be changed. However, there is a possibility that the timer gradually gains or loses time. It is problematic that the time indicated by the timer cannot be set again to the correct one. Further, when the lithium battery of the timer goes dead, it is not possible to record the time.
Further, in this prior art, the manufacturer is supposed to open to the public all the public keys assigned for particular digital cameras. However, when a very large number of digital cameras are manufactured, to open to the public the same number of public keys is troublesome. Further, it is necessary to locate a corresponding public key from a huge public-key list when the integrity of an image is to be verified.
Further, because this prior art relates to digital cameras, which are digital apparatuses for general users, matters such as that who recorded data and so forth have not been considered. For example, especially in a case of a medical measurement apparatus such as a CT (Computed Tomography) apparatus or a digital endoscope, it may be important who measured (took) data.
Further, because this prior art relates to digital cameras which are comparatively inexpensive digital apparatuses for general users and have a short life cycle, matters concerning addition/replacement of the digital-signature algorithm inside of each digital camera and updating of the keys have not been considered. Merely it is disclosed that a new algorithm is loaded in a new product model. However, for example, in a case of an expensive digital medical apparatus such as a CT apparatus, the life cycle thereof is long, and there is a possibility that, over time, the strength of the encryption algorithm may be weakened, that is, the possibility that a code generated using the encryption algorithm is deciphered dishonestly increases in a period shorter than the life of the apparatus.